My brother and sister-in-law use a couple of bluetooth headsets whch regrettably work quite well.
I say 'regrettably' because their chatter was irritating on recent group ride.
Brother would say something that I could hear, leaving me not knowing if he was talking to me or not, then I would hear half the conversation with his wife who was out of my earshot.
If I was riding with one or other of them, they would suddenly say something apparently irrelevant because they were responding to a message in their ear.
It slowly drove me nuts over a 100 mile ride, but happily the batteries on the contraptions conked out after about 75 miles, so I got a bit of relief for the last couple of hours.